Modified oilseed materials are used as food additives for enhancing texture and other functional characteristics of various food products as well as a source of protein. The use of modified oilseed materials such as modified soybean materials may be limited in some instances, however, due to their flavor and/or color characteristics. It is still unclear exactly which components are responsible for the flavor and color characteristics of oilseeds, though a variety of compounds are suspected of causing these characteristics. Among these are aliphatic carbonyls, phenolics, volatile fatty acids and amines, esters and alcohols.
There are extensive reports of processes used for the isolation, purification and improvement of the nutritional quality and flavor of oilseed materials, particularly soybean materials. Soybean protein in its native state is unpalatable and has impaired nutritional quality due to the presence of phytic acid complexes which interfere with mammalian mineral absorption, and the presence of antinutritional factors which interfere with protein digestion in mammals. The reported methods include the destruction of the trypsin inhibitors by heat treatment as well as methods for the removal of phytic acid. A wide variety of attempts to improve the yield of protein secured as purified isolate relative to that contained in the soybean raw material have also been described.
Many processes for improving soy protein flavor involve the application of heat, toasting, alcohol extraction and/or enzyme modification. These types of processes often result in substantial protein denaturation and modification, thereby substantially altering the product's functionality. In addition, these processes can promote interactions between proteins with lipid and carbohydrate constituents and their decomposition products. These types of reactions can reduce the utility of soy proteins in food products, especially in those that require highly soluble and functional proteins, as in dairy foods and beverages.
Commercial soy protein concentrates, which are defined as soy protein products having at least 70% by weight protein (dry solids basis or “dsb”), are generally produced by removing soluble sugars, ash and some minor constituents. The sugars are commonly removed by extracting with: (1) aqueous alcohol; (2) dilute aqueous acid; or (3) water, after first insolubilizing the protein with moist heating. These processes generally produce soy protein products with a distinctive taste and color.
Soy protein isolates are defined as products having at least 90% by weight protein (dsb). Commercial processes for producing soy protein isolates are generally based on acid precipitation of protein. Methods of producing soy protein isolates often include (1) extracting the protein from soy flakes with water at an alkaline pH and removing solids from the liquid extract; (2) subjecting the liquid extract to isoelectric precipitation by adjusting the pH of the liquid extract to the point of minimum protein solubility to obtain the maximum amount of protein precipitate; and (3) separating precipitated protein curd from by-product liquid whey. This type of process, however, still tends to produce a protein product with a distinctive taste and color.
A number of examples of processes for producing concentrated soy protein products using membrane filtration technology have been reported. Due to a number of factors including cost, efficiency and/or product characteristics, however, membrane-based purification approaches have not experienced widespread adoption as commercial processes. Such processes may suffer from one or more disadvantages, such as reduced functional characteristics in the resulting protein product and/or the production of a product which has an “off” flavor and/or an off-color such as a dark cream to light tan color. Membrane-based processes can also be difficult to operate under commercial production conditions due to problems associated with bacterial contamination and fouling of the membranes. Bacterial contamination can have undesirable consequences for the flavor of the product.